Planar displays have great superiority in the portable display device and limited-space display market because they are lightweight and small. To date, in addition to liquid crystal displays (LCD), organic electro-luminescent displays (OLED), and plasma display panels (PDP), a mode of optical interference display is another option for planar displays.
U.S. Pat. No. 5,835,255 discloses an array of optical interference display units of visible light that can be used as a planar display. Referring to FIG. 1, FIG. 1 illustrates a cross-sectional view of a conventional optical interference display unit. Every optical interference display unit 100 comprises a light-incidence electrode 102 and a light-reflection electrode 104 formed on a transparent substrate 105. The light-incidence electrode 102 and the light-reflection electrode 104 are supported by supporters 106, and a cavity 108 is subsequently formed therebetween. The distance between the light-incidence electrode 102 and the light-reflection electrode 104, that is, the length of the cavity 108, is D. The light-incidence electrode 102 is a semi-transmissible/semi-reflective layer with an absorption rate that partially absorbs visible light. The light-reflection electrode 104 is a light reflective layer that is deformable when voltage is applied. The light-incidence electrode 102 comprises a transparent conductive layer 1021, an absorbing layer 1022, and a dielectric layer 1023. When the incident light passes through the light-incidence electrode 102 and into the cavity 108, in wavelengths (λ) of all visible light spectra of the incident light, only visible light with a wavelength λ1 corresponding to formula 1.1 can generate a constructive interference and can be emitted, that is,2D=Nλ  (1.1)
where N is a natural number.
When the length D of the cavity 108 is equal to half of the wavelength multiplied by any natural number, a constructive interference is generated and a sharp light wave is emitted. In the meantime, if an observer follows the direction of the incident light, a reflected light with wavelength λ1 can be observed. Therefore, the optical interference display unit 100 is “open”.
FIG. 2 illustrates a cross-sectional view of a conventional optical interference display unit after a voltage is applied. Referring to FIG. 2, while driven by the voltage, the light-reflection electrode 104 is deformed and falls down towards the light-incidence electrode 102 due to the attraction of static electricity. At this time, the distance between the light-incidence electrode 102 and the light-reflection electrode 104, that is, the length of the cavity 108, is not exactly equal to zero, but is d, which can be equal to zero. If D in formula 1.1 is replaced with d, only visible light with a wavelength λ2 satisfying formula 1.1 in wavelengths λ of all visible light spectra of the incident light can generate a constructive interference, be reflected by the light-reflection electrode 104, and pass through the light-incidence electrode 102. Because the light-incidence electrode 102 has a high light absorption rate for light with wavelength λ2, all the incident light in the visible light spectrum is filtered out and an observer who follows the direction of the incident light cannot observe any reflected light in the visible light spectrum. Therefore, the optical interference display unit 100 is now “closed”.
The light-incidence electrode 102 is a semi-transmissible/semi-reflective electrode. When the incident light passes through the light-incidence electrode 102, a portion of the intensity of the light is absorbed by the absorbing layer 1022. The transparent conductive layer 1021 can be formed from transparent conductive materials such as indium tin oxide (ITO) and indium-doped zinc oxide (IZO). The absorbing layer 1022 can be formed from metals such as aluminum, chromium and silver. The dielectric layer 1023 can be made of silicon oxide, silicon nitride or metal oxide which can be formed by directly oxidizing a portion of the absorbing layer 1022. The light-reflection electrode 104 is a deformable reflective electrode that can move upwards and downwards depending on the applied voltage. The light-reflection electrode 104 is formed from a reflection layer made of metal/transparent conductive material and a mechanical stress adjusting layer. Typical metals used in forming the reflection layer include silver and chromium. However, silver has a low stress, and chromium has a high stress but the reflectivity thereof is quite low. Therefore, there exists a need to use a highly reflective metal to form the reflection layer and a high stress metal to form the mechanical stress adjusting layer thereby allowing the light-reflection electrode 104 to become a displaceable and reflective electrode.
The display apparatus formed from the array of optical interference display units of visible light is Bi-Stable and is characterized by having low power consumption and much shorter response time. Therefore, it can be used as a display panel and is especially suitable for use in portable equipment such as mobile phone, PDA, portable computer, and so on.